Cross-flow blowers, sometimes called tangential blowers, or squirrel cage blowers, have been known for more than 100 years. FIG. 2 is an 1892 sketch of such a blower by Mortier. These blowers have a generally hollow cylindrical shape with a large number of blades located at the circumference. They were used extensively for mine ventilation in the early 1900s, but were soon replaced in the mines by blowers of other design. Interest in cross-flow blowers increased in the mid-1900s, and the blowers have been used in many applications in recent years. Cross-flow blowers are most often chosen when high flow, low head circulation is needed.
A prior art application of cross-flow blowers is to circulate the gas gain medium between two elongated electrodes in excimer lasers. An example of this use is described in U.S. Pat. No. 5,023,884 assigned to the Applicant's employer. This laser is useful as the light source in laser lithography equipment used in integrated circuit fabrication. As indicated in FIG. 1 (also FIG. 1 in the '884 patent), the laser gas is circulated through a discharge region 22 between two elongated spaced apart electrodes 18 and 20. The discharge region is about 5/8 inch and 28 inches long. The gas circulation is provided by a cross-flow blower 46 which is about 4 inches in diameter and about 28 inches long.
These excimer lasers have, in the past, operated in a pulse mode at rates of up to 1,000 Hz. A pulse rate of 1,000 Hz requires a flow rate of gas between the electrodes of at least about 2,000 cm/second in order to assure that "old gas" from one pulse is cleared from the discharge region before the beginning of the next pulse. Gas speeds of about 2,000 cm/second requires a fan speed of about 3,300 rpm. At speeds greater than 3,300 rpm, the long skinny fan develops vibrational modes that lead to rapid bearing failure and sometimes sufficient distortion to damage the structural elements of the fan itself.
Efforts have been made to make the fan more rigid. These efforts include improved manufacturing processes and the use of materials having increased strength. To the best of Applicant's knowledge, all prior art efforts to strengthen these blowers have left the inside of the blower hollow. This may have been the result of a prior art assumption that hollow insides are required for proper functioning of cross-flow blowers.